Can you please explain the outbreeding devices of pollination?
Repeated self pollination leads to inbreeding depression. Methods or devices which favor cross pollination are known as outbreeding devices.
Plants have developed methods to prevent self pollination. Autogamy is prevented by following ways:
- Pollen release and stigma receptivity not coordinated
- Different positioning of the anther and the stigma
- Production of unisexual flowers
Ways to prevent both autogamy and geitonogamy:
- Presence of male and female flowers on different plants, such that each plant is either male or female (dioecy).
- This mechanism is present in several species of papaya.
First of all what are outbreeding devices n why r they necessary-
Devices that discourage SELF-POLLINATION & encourage CROSS-POLLINATION are known as outbreeding devices.
They r necessary bcuz continued SELF-POLLINATION in flowers causes a downfall in the quality and variety of the products.
There are 4 types of outbreeding devices-
1.) Release of Pollen much before or much after the stigma is ready to accept it (receptiveness of stigma) .
2.) Placement of anther & stigma at such positions so that the pollens do not reach the stigma of the same plant or the same flower.
3.) It is a chemical method in which the stigma inhibits the growth of the pollen tubes into the pistil. This process is known as SELF-INCOMPATIBILITY
4.) Production of flowers or plants that are UNISEXUAL i.e. the plant or flower exhibit dioecy.
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Out breeding devices are:-
- Monoecious Condition:
- Male and female plants are seen on the same plant. In this case autogamy can be avoided but not geitonogamy.
- Male plants and female plants are formed. i.e. male plants produce male flowers and female plants produce female flowers only. Both autogamy and geitonogamy can be prevented in these plants.
Anther and stigma mature at different times.
- Protandry: Anthers mature first. e.g. Sunflower, Cotton, Salvia
- Protogyny: Stigma matures first. e.g. Mirabilis, Gloriosa
- The pollen grain of a flower cannot germinate or develop on the stigma of the same flower. e.g. Sunflower, Mustard, Potato, Tobaco etc.
- Prepotency: Pollen grains of other flowers germinate more rapidly than that of the same flower
- Carpels and stamens are arranged at different heights to prevent the falling of pollen on the surface of the stigma of the same flower. E.g. Oxalis, Gloriosa, Jasmine
- Anther and stigma are developed at different positions. E.g. Gloriosa, Clerodendron